This invention relates to a method of transferring signals within an electronic control system for internal combustion engines and, more particularly, to a method of transferring signals between central processing units, one for controlling the amount of fuel injection and another for controlling the ignition timing.
A control system for electronically controlling such items as the amount of fuel injection and ignition timing of an internal combustion engine is already known, e.g. from Japanese Provisional Patent Publication (Kokai) No. 53-76231, wherein the electronic control system is equipped with a single central processing unit (hereinafter referred to as a "CPU") supplied with input signals indicative of various engine operating parameters such as engine coolant temperature and absolute pressure in the engine intake pipe, a crank angle signal generated whenever the engine crankshaft rotates through a predetermined angular increment, and a reference position signal, two pulses of which are generated per revolution of the crankshaft. On the basis of these input signals, the single CPU executes two separate sets of computations, one related to control of fuel ignition quantity and the other related to control of ignition timing.
In recent years efforts have been made to meet the demand for improved drivability. This has resulted in more complex operational programs for each of quantities that are to be controlled, such as fuel injection quantity and quantity related to fuel injection timing, and, hence, in a heavier processing load upon the CPU.
Consequently, when it is attempted to have a single CPU execute the processing needed to control a plurality of quantities such as fuel injection quantity and fuel injection timing, it is no longer possible to deal with an increase in processing load associated with each quantity. In particular, the demand for engine control of greater precision cannot be met by a single CPU at high engine rotation, where the time available for processing is less than that which can be used when the engine is rotating at low speed. Though this demand can in fact be satisfied if use is made of a CPU having a very high processing capability, such as a 32- or 64-bit CPU, this expedient is impractical because of the high cost involved.
On the other hand, if a plurality of CPU's are employed in order to simultaneously execute the processing needed to control a plurality of quantities such as fuel injection quantity and quantity related to fuel injection timing, each CPU has to be provided with one set of engine operating parameter sensors, an input circuit, etc. for inputting engine parameter values necessary for the control by the CPU. As a result, as many sets of such sensors, as many input circuits, etc. as the number of CPU's are required, which results in an electronic control system having a very complicated and bulky construction, making it difficult to perform assembling and maintenance.
However, if, for those engine operating parameters whose values are required to be used by two or more CPU's, only one set of sensors, an input circuit, etc. are provided to detect and supply the parameter values to one of the CPU's and if this CPU is made capable of transferring the parameter values to the other CPU or CPU's, there will be no need of providing as many sets of sensors, as many input circuits, etc. as the number of CPU's for those engine operating parameters. But a problem arises with transfer of data such as engine operating parameter values between the CPU's that if data consisting of a plurality of bits are to be transferred at one time upon a timing signal, i.e., if a parallel synchronous data transfer method is applied, as many signal lines as the number of bits constituting the data frame will be required, which in turn requires use of as many pairs of terminals of the CPU's which are limited in number. Also, the above method essentially requires the two CPU's to be operated synchronously with each other to transfer data from one CPU to the other, thus requiring complicated control programming.